Low Cost Limited Rotation Rotary Actuator

ABSTRACT

A limited rotation electromechanical rotary actuator includes a stator having an aperture sized to accept a rotor assembly and a rectangular coil. A rotor assembly is bidirectionally operable with the stator over a limited range of rotation. The rotor assembly includes an output shaft and a two-pole magnet and a position sensor shaft, wherein the output shaft and position sensor shaft are each rigidly attached to only a portion of the magnet. The rotor assembly includes apertures for allowing an electrical coil to pass through. The electrical coil extends around the magnet on four sides and is excitable for providing bidirectional torque to the rotor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/112,755, having filing date of Feb. 6, 2015 the disclosure of whichis hereby incorporated by reference in its entirety and commonly owned.

FIELD OF THE INVENTION

The present invention generally relates to limited angleelectromechanical rotary actuators and in particular to actuators usedin the field of optical scanning.

BACKGROUND

Limited-angle, electromechanical rotary actuators have been in existencefor decades. They are used in a variety of industrial and consumerapplications, but they are particularly useful in the field of opticalscanning, where an optical element is attached to an actuator outputshaft, and is then rotated back and forth in an oscillating manner.

For example and as illustrated with reference to FIG. 1, it is common toattach a mirror to the output shaft of a rotary actuator in order tocreate an optical scanning system. In this application, theactuator/mirror combination can redirect a beam of light through a rangeof angles, or redirect the field of view of a camera so that it canobserve a variety of targets.

Typical electromechanical rotary actuators used in the field of opticalscanning are generally made from some combination of magnet, steel andcoils of insulated “magnet” wire. These elements have been arranged in avariety of ways, but for the past twenty years, the most populararrangement has been to use a simple two-pole rotor magnet, and a“toothless” stator design, similar to a slotless/brushless DC or ACsynchronous motor, but having a simpler, single-phase coil arrangement.

The rotor within these actuators is typically made of a cylindricalmagnet, onto which one or two shafts are attached in one way or another.Several known rotor assemblies are illustrated by way of example withreference to FIGS. 2, 3 and 4.

When this type of actuator is used for optical scanning, one shaft maybe attached to a mirror and another shaft operable with a positionsensor. The rotor assembly is typically supported on one side or bothsides by ball bearings.

It will be helpful to review known actuator technology and makereference to known actuators to have the reader better understand theneeds satisfied by embodiments of the present invention.

FIG. 5 illustrates a sectional view of a rotor magnet, stator and coilarrangement found in a typical conventional optical scanner of currentstate of the art. The stator is essentially tubular and made from asolid piece of magnetically conductive material such as cold rolledsteel. For the rotor magnet having a diameter of 0.120 inches, a typicalstator tube may have an outside diameter of 0.5 inches (around 12.7millimeters), and an inside diameter of 0.196 inches (approximately 5millimeters). The coil is made of turns of magnet wire, bonded to theinside wall of the stator steel tube using epoxy. Each side of the coilis formed as an arc, often occupying an approximately 90-degree arc oneach side of the stator as herein illustrated. There is typically arounda 0.007 inch gap between the outside wall of the rotor magnet and theinside wall of the coil, thus allowing the magnet to rotate freely. Withcontinued reference to FIG. 5, the coil areas are designated “Coil plus”and “Coil minus” to indicate turns going into the page and turns comingout of the page, respectively.

FIG. 6 illustrates magnetic field lines found in a conventional opticalscanner of the current state of the art as illustrated in FIG. 5, usinga solid cylindrical diametral-magnetized rotor magnet. It can be seenthat the magnetic flux lines must extend (“jump”) across a relativelylarge gap to reach the stator steel. The coil resides in between themagnet and the stator steel. When the coil is energized, a Lorentz Forceis imposed on both the coil and the magnet. Since the coil is typicallybonded to the stator and thus, held stationary, all of the force isconveyed to the rotor magnet. Since force is created on opposite sidesof the magnet, the force being in the form of torque, the actuatorcreates torque and thus creates motion.

FIG. 9a illustrates one cylindrical rotor magnet and coil windings. Asshown, the magnet essentially resides “inside” the coil. Steel whichresides outside the coil is not shown in this illustration. The coilincludes multiple turns of magnet wire. The long, straight portion ofthe coil is known as the “active portion” because this is the portionwhich contributes to torque on the magnet. The rounded portion of thecoil is known as “end-turns”. The end turns do not contribute to torqueproduction. They are merely there to connect the active portion on oneside of the coil to the other side of the coil. However, any heating ofthe drive coil that results from current passing through it, also existsin the end turns. Thus, while the end turns do not contribute to torqueproduction, they do contribute to heat, ohmic resistance and electricalinductance, all attributes which are detrimental to overall actuatorperformance. Therefore, there is motivation to keep the end-turns asshort as possible in order to minimize these detrimental effects.

By way of further example with reference again to FIG. 9a , the coil isshown having its coil windings completely surrounding the magnet on top,bottom, left and right portions. This coil arrangement is typically notused in known actuators because the end turns as diagrammaticallyillustrated in this FIG. 9a would prevent a shaft from reaching themagnet. Instead, the end turns must be bent out of the way (or rather“formed”), as illustrated with reference to FIG. 9b . When the end-turnsare formed in this way, this typically allows for the shaft (which isattached to the magnet) to “pass through” the end turns and result inwhat is effectively a “hole” formed in the coil. Of course, this meansthat the “end-turns” must be made undesirably longer in order to createsuch a “hole”. As will be illustrated later in the teachings of thepresent invention, such an undesirable feature is eliminated inactuators herein presented by way of example.

Such a conventional actuator arrangement provides some desirablebenefits. One benefit is the relatively low coil inductance that resultsfrom the fact that the coil does not completely surround a closed steelcore. Quite the contrary, the entire inside of the actuator is open,containing only the rotor magnet whose permeability is almost the sameas that of air. Another benefit is that the rotor generally has no“preferred position”, meaning that once the rotor is positioned, powercan be removed from the coil and the rotor will remain in that position.For optical scanning applications, the performance of this type ofactuator is well suited for applications including laser marking andsome laser graphic projection.

However, although this conventional actuator structure has been usedsuccessfully for optical scanning for more than two decades, the costsinvolved in forming the coil and then bonding the coil to the statorhave prevented this type of actuator from being highly successful incertain consumer-grade applications, including point-of-purchasedisplays, 3D printers, and certain self-driving and assisted-drivingautomobiles, where low cost is paramount.

For the type of actuator whose arrangement is shown in FIG. 5 and endturns formed as above presented in FIG. 9b , the coil is the mostdifficult and thus most costly part to manufacture, because ideally, itmust be wound in three dimensions. Coils of this type are generallyshown in FIG. 2a of U.S. Pat. No. 4,090,112 (item 50); FIG. 1 of U.S.Pat. No. 5,313,127 (item 30); FIG. 8 of U.S. Pat. No. 5,424,632 (item75); and FIG. 4 of U.S. Pat. No. 6,633,101 (item 34 and 42). Althoughsome of the figures show all of the individual coil turns neatly formedand having very good copper packing, such coil windings are typicallyknown not to be this neat. Because of the 3D nature of the coil winding,the individual turns often effectively compete for space, with turns“crossing over” each other, thus leading to sub-optimal current densitydistribution as well as sub-optimal heat sharing among the turns of thecoil.

Nevertheless, once the coil is formed, inserting it into the stator isthe next challenge. Because of the close proximity of the stator wall tothe coil windings, the insulation on the coil can be scratched duringthe insertion process, leading to an instant, or latent “coil-to-caseshort” type of electrical failure.

Bonding the coil to the stator walls is another difficult manufacturingstep for this type of actuator. Thermally-conductive epoxy is often usedto bond the coil to the inside of the stator walls, but very often, airbubbles are formed in the bond, leading to sub-optimal heat removal. Therequired epoxy curing time presents another challenge.

Absent some external angle-limiting element, it is known that thesetypical actuators can spin freely within the stator, and take on anyrotational position. However, this is undesirable for optical scanningapplications because these applications only exercise a mirror over arelatively limited range of angles—generally no greater than 40 degreesmechanical peak-to-peak. Moreover, when a single coil is used along witha two-pole magnet, a desirable torque is not produced at all rotationalangles, and in fact no torque at all is produced at certain angles. Forthese reasons, an external rotational limit is imposed on this type ofactuator. Most often, this limit is imposed by a “stopping pin”, whichis driven through one of the shafts, and which engages externalstationary elements. Stopping pins of this sort are shown in FIG. 1 ofU.S. Pat. No. 5,936,324 (item number 32); and FIG. 2 of U.S. Pat. No.5,424,632 (item number 18).

When a stopping pin is used, the axial length of the shaft mustnecessarily be extended to make room for it. A hole is drilled in theshaft where the stopping pin resides. Although the stopping pin doeslargely fill the hole, it does not completely fill the hole. Therefore,the combination of a longer shaft plus the hole drilled for the stoppingpin weakens the shaft, and undesirably lowers torsional and bending-moderesonant frequencies.

When using this type of conventional actuator for optical scanningapplications, the costs involved in forming, inserting, and retainingthe coil present a genuine limit to how inexpensive an optical scannercan be made, and this limit has prevented certain consumer-grade laserscanning applications from flourishing. For this reason, there isclearly a need for an electromechanical rotary actuator that generallyprovides all of the benefits of this type of conventional actuator foroptical scanning applications, while also having lower manufacturingcosts.

With reference again to FIGS. 7 and 8, one known actuator illustrated inU.S. Pat. No. 4,319,823 is designed for camera shutter applications. Inthis actuator, the coil is rectangular and surrounds the magnet, and ashaft is attached to the shaft using an intermediate, U-shaped member.Unfortunately, because of the way only a single shaft is used and theway in which the shaft is attached to the magnet, this actuator couldnot be used for high-performance optical scanning applications,especially if those applications also required rotor positioninformation.

The above referenced patent publications including: U.S. Pat. No.4,090,112 for Electrically Damped Oscillation Motor (apparently thefirst “moving magnet” type of optical scanner); U.S. Pat. No. 5,313,127for Moving Magnet Motor (a moving magnet type actuator); U.S. Pat. No.5,424,632 for Moving Magnet Optical Scanner with Novel Rotor design toMontagu (a moving magnet scanner and rotor assembly having a stoppingpin); U.S. Pat. No. 5,936,324 to Montagu for Moving Magnet Scanner(motor employing stopping pin item); U.S. Pat. No. 6,633,101 to Stokesfor Moving magnet Torque Motor (an actuator: U.S. Pat. No. 7,365,464 toBrown for Composite Rotor and Output Shaft for Galvanometer Motor andMethod of Manufacture Thereof (a rotor assembly method similar toMontagu); and U.S. Pat. No. 8,569,920 to Ramon et al. for Small ElectricMotor (commonly used rotor assembly and method) are presented by way ofexamples and are herein incorporated by reference in their entirety.

SUMMARY

In keeping with the teachings of the present invention, a limitedrotation electromechanical rotary actuator may comprise a stator, arotor assembly bidirectionally operable within the stator, and a singlecoil whose shape is generally rectangular. The electrical coil surroundsa rotor magnet on the top, bottom, and two sides.

The rotor assembly may include an output shaft, a solid cylindricaldiametral-magnetized magnet and a position sensor shaft. The outputshaft and position sensor shaft each include an aperture where theelectrical coil can pass through while still allowing the rotor assemblyto rotate.

BRIEF DESCRIPTION OF DRAWINGS

For a fuller understanding of the invention, reference is made to thefollowing detailed description, taken in connection with theaccompanying drawings illustrating various embodiments of the presentinvention, in which:

FIG. 1 illustrates a typical optical scanner, wherein a mirror is placedonto an end of an actuator shaft;

FIG. 2 illustrates one type of known rotor assembly, as described inU.S. Pat. No. 5,424,632, wherein two shaft-ends are attached to asleeve, with a rotor magnet contained within the sleeve;

FIG. 3 illustrates another type of known rotor assembly, as described inU.S. Pat. No. 6,633,101, wherein a single shaft end is attached to themagnet, and wherein the shaft end is completely cylindrical, essentiallyforming a “cup” into which the magnet is fully inserted;

FIG. 4 illustrates yet another type of known rotor assembly, wherein themagnet is tubular, having a hole through it through which a solid shaftpasses;

FIG. 5 illustrates a sectional view of an arrangement of rotor magnet,stator steel and coil placement in a known actuator;

FIG. 6 illustrates a magnetic field lines in the arrangement shown inFIG. 5, if a solid cylindrical diametral-magnetized magnet is used;

FIGS. 7 and 8 illustrate a known actuator as described in U.S. Pat. No.4,319,823, having magnet and coil winding with end turns;

FIG. 9a is a diagrammatical illustration of a coil wound around acylindrical magnet is one desirable manner to avoid having to form endturns for receiving a shaft;

FIG. 9b illustrates another arrangement of cylindrical rotor magnet andcoil windings, wherein the end-turns are formed to allow the magnet androtor shaft to pass through;

FIG. 10 illustrates a sectional view of an actuator according to theteachings of the present invention;

FIG. 11 illustrates another sectional view of the embodiment of FIG. 10,wherein in a plane of the sectional view is oriented 90-degrees comparedto FIG. 10;

FIG. 12. is an exploded view of an actuator according to the teachingsof the present invention;

FIG. 13 is a diagrammatical illustration of a rotor assembly operablewith the actuator of FIG. 11 according to the teachings of the presentinvention;

FIG. 14 illustrates one embodiment of a rotor assembly according to theteachings of the present invention;

FIG. 14a is a partial cross-sectional view taken through lines 14 a-14 aof FIG. 14 illustrating a range of rotation limited within a regionbetween coil sides, by way of example;

FIG. 15 illustrates another embodiment resulting from a method offorming the rotor assembly;

FIGS. 16a, 16b and 16c illustrate yet another embodiment, wherein arotor assembly includes a magnet having notches or slots on each end andshafts having cup-type engagements;

FIG. 17a and FIG. 17b illustrate views of a coil holder hereinimplemented as a slotted, cylindrical coil holder;

FIG. 18 illustrates magnetic field lines in an embodiment of the presentinvention when the rotor magnet is a solid, cylindricaldiametral-magnetized magnet and when the coil holder is made of amaterial not made from magnetically conductive material for effectivelyforming a slotless actuator; and

FIG. 19 illustrates the magnetic field lines in the present inventionwhen the rotor magnet is a solid, cylindrical diametral-magnetizedmagnet and the coil holder is made of a material that is made frommagnetically conductive material for effectively forming a slottedactuator.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

Referring initially to FIGS. 10, 11, 12, one embodiment of the presentinvention is herein described as an electromechanical, limited rotation,rotary actuator 10. The actuator 10, herein described by way of example,includes an actuator body 12 which contains the stator 14, wherein thebody may be integrally formed with the stator. The stator 14 has a boreor hole 16 extending axially therein which may be drilled into thestator, the hole being large enough to fit a rotor assembly 18 as wellas a rectangular coil 20, top bearing 22, bottom bearing 24, and coilholder 26, by way of example. Note that in some embodiments, the topbearing 22 or bottom bearing 24 may have an outside diameter larger thanan overall dimension of the hole 16 and thus, the hole may have portionswhich are larger to accommodate the bearings. As further illustratedwith reference to FIG. 12, a bearing preload spring 28 may be employed.

Referring now to FIGS. 13 and 14, the rotor assembly 18 for theembodiment herein described by way of example includes an output shaft30, a magnet 32, and a position sensor shaft 34. The output shaft 30 isrigidly connected to a portion of the magnet 32, preferably with amajority of attachment on an outside periphery 36 (i.e. diameter) of themagnet. As herein described by way of example, the shaft 30 includes aconnection 31 extending from a body portion of the shaft. With referenceto FIG. 14a , the connection 31 is dimensioned to extend partiallyaround a peripheral surface of the magnet 32. The position sensor shaft34 is also rigidly connected to a portion of the magnet 32 on an axialopposite end 38, preferably with a majority of the attachment happeningon the outside periphery 36 of the magnet 32. The shaft 34 as hereindescribed by way of example includes a connection 35 extending from abody portion of the shaft 34. With reference again to FIG. 14a , it willbe understood by those of skill in the art now having the benefit of theteachings of the present invention that the connection 35 is dimensionedto extend partially around a peripheral surface (periphery 36) of themagnet 32 and may be sized as is the connection 31 for maintaining thedesired range of rotation 19. With continued reference to FIG. 14a , therotor assembly 18 is bidirectionally operable over a limited range ofrotation 19 with the stator 14, and extends into the hole 16. By way ofexample for the embodiment herein described, the limited range ofrotation 19 will be determined generally by an arc length of theconnectors 31, 35 such that the shafts 30, 34 can be rotated betweenopposing sides of the coil 20 without the connectors 31, 35 hitting theopposing sides of the coil. For the embodiment herein illustrated withreference to FIG. 14a , the connector 31 is rotated between opposingactive coil portions. While the connectors 31, 35 illustrated withreference to FIG. 14a , by way of non-limiting example, are formed as asingle continuous structure, it will come to the mind of those skilledin the art, now having the benefit of the teachings of the presentinvention, to form the single connectors 31, 35 as a plurality ofconnectors, wherein the outer connectors within the plurality ofconnectors define the arc length and thus the limited range of rotation19. Further, and as illustrated with reference again to FIGS. 11 and 13,the connectors 31, 35 may comprise connector pairs. Yet further, whileit is desirable to have the connectors 31, 35 substantially contactingthe outer cylindrical surface of the magnet 32, as illustrated for theembodiments herein described, it will be understood by those of skill inthe art that a portion of the top and bottom of the magnet may becontacted by the connectors 31, 35 without departing from the essenceand teachings of the present invention. The coil is out of contact withthe magnet, thus avoiding frictional contact therewith.

In the embodiment shown in FIG. 13, the magnet 32 is a two-pole, solidcylindrical diametral-magnetized magnet. Although there are several waysto form a rotor using a magnet, the use of a solid, cylindricaldiametral-magnetized magnet provides desirable benefits. One benefit isthat a sinusoidal flux-versus-angle (here the “angle” being with respectto the magnet itself) profile results from the magnet. This in turnproduces an approximately sinusoidal output-torque versus rotormechanical angle profile of the actuator 10 when current is applied tothe coil 20. Nevertheless, other magnet shapes may be used and stillremain within the spirit and teachings of the present invention,including a square and a rectangular shaped magnet, as long as themagnet has two poles arranged so that they coincide with the activeportion of the rectangular coil 20. By way of further example, referenceis again made to FIG. 10 illustrating the active coil portions 20R and20L in close proximity to the North and South poles of the magnet 32.

In known actuators used in the field of optical scanning, the shaftstypically pass axially through to the rotor magnet, essentially formingan un-broken and continuous connection of the shaft through the magnetaxis. However, with embodiments of the present invention as hereindescribed by way of example, the rotor assembly 18 provides an aperture40, 42 for the coil 20 to pass through, the aperture residing througheach shaft 30, 34 as shown with continued reference to FIGS. 13 and 14,and now to FIG. 15, or alternatively through slots 44, 46 in the magnet32 as shown in FIGS. 16a, 16b and 16c . The apertures 40, 42 provide afree space between the shaft 30, 34 and the coil 20 and between the coil20 and the magnet 32. In the embodiments herein described by way ofexample, this aperture 40, 42 is facilitated through the fact that theoutput shaft 30 and the position sensor shaft 34 attach to only aportion of the magnet 32, and such attachment is made to outer surfaces32L, 32R of the magnet 32 by way of example, thus shafts desirably nottouching a center portion of top 32T and bottom 32B surfaces of themagnet proximate the longitudinal axis 33 of rotation.

With further emphasis, for the rectangular coil 20, herein described byway of example, with reference to the embodiments herein described, itis clear and desirable that material from the shafts 30, 34 does nottouch the top and bottom surfaces 32T, 32B of the magnet 32 at orproximate the longitudinal axis, as illustrated with reference again toFIG. 14. End turns of the coil 20 are also out of contact with themagnet 32 at the top and bottom surfaces. In contrast, and typically inthe art, structural elements make contact with the axis of the magnet.By way of example with reference to the above referenced U.S. Pat. No.4,319,823, a U-shaped member touches the axis and the entire top surfaceof the magnet. For other well-known actuators, a shaft is typicallyaligned with the magnet and passes at least partially through the magnetalong its axis. While sensors may not be attached, contact with themagnet will typically be used for aligning and pivoting the magnet.

FIGS. 16a, 16b and 16c illustrate an alternative embodiment for formingthe rotor assembly 18 according to the teachings of the presentinvention. In this embodiment, the magnet 32 is a two-pole, cylindricaldiametral-magnetized magnet, having the 44, 46 cut into top and bottomportions 32T, 32B. The output shaft 30 and the position sensor shaft 34are each rigidly connected to the magnet 32 at outer portions of theslots 44, 46. In this embodiment of the rotor assembly 18, the shafts30, 34 are relatively easier to make, having simple cup-like engagementareas. Note that in this embodiment, it is the magnet 32 which providesthe apertures 40, 42 through which the coil 20 can pass.

With reference again to FIG. 10, it can be clearly seen that theelectrical coil 20, herein embodied as a rectangular shaped coil by wayof non-limiting example, surrounds the magnet 32 on top, bottom, leftand right side thereof. Using the coil terminology established above,the left side 20L and right side 20R of the coil 20 are the “activeportions” and the top side 20T and the bottom side 20B of the coil 20are the “end-turns”. The rectangular coil 20 herein described by way ofexample is excitable for providing bidirectional torque to the rotorassembly 18.

Since the two-pole magnet 32 is used, by way of example, along with thesingle electrical coil 20 whose active portions resides on only twosides 32L, 32R of the magnet 32, maximum rotor torque output occurs whenthe north and south poles of the magnet are in closest proximity to eachactive portion of the electrical coil, and minimum (essentially zero)torque occurs when the north and south poles of the magnet are at a90-degree angle to the active portion of the coil, as illustrated withcontinued reference to FIG. 10.

The inside dimensions of the coil 32 are chosen to provide a gap 48around the magnet 32, which is herein referred to as free space betweenthe magnet and the coil. This gap 48 is preferably made as small aspossible because as this gap increases, coil area (where turns of wirecan be placed to create torque) effectively decreases. For the actuator10 shown in FIG. 10 and FIG. 11, this gap 48 is around 0.006 inches allthe way around the magnet 32, but this should not be construed as alimitation.

The outside dimensions of the coil 20 are chosen to be small enough tofit into the hole 16 in the stator, and also small enough to work withthe aperture 40, 42 for the coil to pass through, ultimately providingthe free space between the shaft 40, 42 and the coil.

As illustrated with continued reference to FIG. 10 and FIG. 11, for boththe output shaft 30 and the position sensor shaft 34, there is the gap48 providing the free space between the shaft 30, 34 and the coil 20,and also a free space between the coil and the magnet 32. These freespaces are effectively provided by the aperture 40, 42 for the coil 20to pass through, and allows for the rotor assembly 18 to rotate freelyover a limited range of rotation.

By way of example, this aperture 40, 42 for the coil 20 to pass throughworks together along with the thickness of the electrical coil to definethe range of operating angles for the actuator 10, because the aperturefor the coil to pass through must be large enough to allow the coil topass through while also allowing the rotor assembly 18 to rotate. As theaperture 40, 42 for the coil 20 to pass through is made larger, therotor assembly 18 is able to rotate through a greater range of angles.However, increasing the size of the aperture 40, 42 for the coil 20 topass through also consequently decreases an amount of shaft materialthat remains in rigid connection with the magnet 32, thereby making theoverall rotor assembly 18 weaker. Therefore, the coil 20 dimensions andsize of the aperture 40, 42 for the coil to pass through must be tradedoff as desired to accomplish the desired limited rotation angle of theactuator 10 and desired strength and stiffness of the overall rotorassembly 18.

With continued reference to FIG. 10 and FIG. 11, it is clearly shownthat the output shaft 30 and the position sensor shaft 34 attach to themagnet 32 at primarily two places. As will be understood by those ofskill in the art, the shape of the attaching area depends on the shapeof the magnet 32 (i.e. if it is cylindrical or more cubical). If themagnet 32 is cylindrical, then the output shaft 30 and the positionsensor shaft 34 preferably attach to the magnet 32 at mating arc-shapedareas, primarily around the outer diameter of the magnet. If the magnet32 is cubical, then the output shaft 30 and the position sensor shaft 34preferably attach to the magnet 32 on two flat sides of the magnet.

Typically, the output shaft 30 and the position sensor shaft 34 would beattached to the magnet 32 using an adhesive such as an epoxy. Adhesivesused in embodiments herein described have included anaerobic adhesivesand cyanoacrylate, by way of non-limiting example. By way of furtherexample with reference again to FIG. 11, the output shaft 30 and theposition sensor shaft 34 both attach primarily to the magnet 32 on theleft side 32L and right side 32R of the magnet. In FIG. 11, it can beseen that the output shaft 30 and the position sensor shaft 34 do notattach to the magnet 32 at the rear 32RR or front side 32F of themagnet. The rear and front sides 32RR, 32F are where the aperture 40, 42for the coil 20 to pass through resides. Although the output shaft 30and the position sensor shaft 34 are not attached to the magnet 32 onall surfaces, this rotor assembly 18 and assembly forming method aresufficiently strong for many applications, including optical scanning.In fact, computer simulation followed by testing showed that rotorstiffness of this configuration is as desirable as conventional movingmagnet galvanometer scanners.

In order for the rectangular coil 20 to surround the magnet 32 as shownin FIG. 10 and FIG. 11, this places a constraint on the order in whichthe actuator 10 is assembled. To assemble the rotor assembly 18 of theactuator 10 shown in FIG. 10 and FIG. 11, the rectangular coil 20 isfirst placed loosely around the magnet 32 t, and then the output shaft30 and the position sensor shaft 34 are attached to the magnet (forexample using epoxy). The rotor assembly 18 and the coil 20 combinationare then inserted into the hole 16 of the stator 14 and the coil 20 isheld in place using the coil holder 26 or coil holding means.

However, this may make assembly of the rotor assembly 18 somewhatcomplicated. An assembler must manage axially fixing the output shaft 30and the position sensor shaft 34 onto the magnet 32 while the coil 20 isloosely in place. Care must be taken to make sure no adhesive (if used)gets on the rectangular coil 20, thus avoiding impeding free rotation.

As an alternative, the output shaft 30 and the position sensor shaft 34may be embodied in such a way that they only attach to a single side ofthe magnet 32 rather than two sides. This is shown in alternateembodiments illustrated with reference to FIG. 14 and FIG. 15. In thesecases, the aperture 40, 42 for the coil 20 to pass through includes notonly a free space between the magnet 32 and the coil and a free spacebetween the shaft 30, 34 and the coil, but also a completely open side,through which the coil may be inserted after the output shaft 30 and theposition sensor shaft 34 are already attached to the magnet 32. By wayof non-limiting example, FIG. 14 illustrates one possible embodiment inwhich the output shaft 30 and the position sensor shaft 34 are attachedto the magnet 32 on the same side (here on the left side 32L asillustrated in the drawing view). Because of this, the rotor assembly 18can be completely formed without the coil 20, and then later therectangular coil 20 can be placed into the assembly 18 from the right,by way of example. Yet further, FIG. 15 illustrates another possibleembodiment in which the output shaft 30 and the position sensor shaft 34are attached to the magnet 32 on opposite sides. In this case, once therotor assembly 18 is completely formed, the coil 20 can be brought infrom the top or the bottom and then rotated into position. Of course,the rotor assemblies 18 shown in FIG. 14 and FIG. 15 may not be asstrong as the rotor assemblies shown in FIG. 13 and FIGS. 16a, 16b and16c because there is less shaft material in contact with the magnet 32,assuming a similar adhesive is used. Therefore, there is a trade-offbetween rotor stiffness/strength and ease/order of assembly.

In any event, since the magnet 32 is supported at the top and bottom byseparate shafts 30, 34, the rotor assembly 18 embodiments describedherein achieves a level of stiffness that has proven to be acceptablefor optical scanning applications, with the rotor assemblies shown inFIG. 13 and FIGS. 16a-16c being as desirable as those of conventionalmoving magnet galvanometer scanners, while also having similar inertia.This is counter-intuitive, since placing an aperture 40, 42 in betweenthe magnet 32 and each shaft 30, 34 would intuitively tend to reducestiffness. Stiffness is maintained by ensuring a liberal amount ofcontact area between the magnet 32 and the output shaft 30, as well asthe magnet and the position sensor shaft 34, and by fixing the magnet toeach shaft around the outer periphery of the magnet. Stiffness is alsomaintained due to the fact that each shaft 30, 34 is directly affixed tothe magnet 32, instead of using some intervening element between eachshaft and the magnet. As described above with reference to connectors31, 35 of the shafts 30 and 34, similar connectors 31, 35 may be formedusing the material of the magnet, as illustrated with reference again toFIG. 16 b.

By way of further example, to maximize fatigue resistance while also notinterfering with the magnetic flux produced by the magnet 32 andelectrical circuit of the coil 20, the output shaft 30 and the positionsensor shaft 34 may be made from a non-magnetic Stainless Steel such asgrade 303, but this is not intended to be a limitation. Other materials,including even plastic materials such as Delrin, Nylon or PEEK can beused when rotor stiffness is not a paramount concern.

In this example embodiment, the actuator body 12 is formed as the stator14, and is a simple, tubular shape. To maximize torque output from theactuator 10, the stator 14 is made of a magnetic conductive material.One possible inexpensive material that will work effectively is coldrolled steel such as 1018 steel, but magnetic stainless steels will alsowork effectively, such as 416 or 430. When it is desirable to minimizepositional hysteresis (but at a much greater stator material expense),Carpenter 49 nickel-steel can be used.

Alternatively, the stator 14 may not include any magnetic conductivematerial at all, and may by way of example, be made out of plastic suchas Delrin, Nylon or PEEK. When the stator 14 does not include magneticconductive material the actuator 10 will produce considerably lesstorque—perhaps less than half of that when using magnetic permeablematerial. However, electrical inductance of the rectangular coil 20 willalso be correspondingly reduced, and therefore for certain applications,making the stator 14 from a non-magnetic-conductive material may bedesirable.

Further, the rectangular coil 20 may be held in place within the stator14 using a variety of means. However, in the embodiment illustrated byway of example in FIG. 10 and FIG. 12, coil holding means, the coilholder 26, is implemented as a slotted, cylindrical coil holder. Thismay be a tubular element whose inside diameter is large enough for therotor assembly 18 to pass through, and whose outside diameter is smallenough to fit within the hole/bore 16 of the stator 14. This tubularelement has at least a coil slot 50 on diametrically-opposed sides,sufficient for the rectangular coil 20 to slide into and be held inplace, as illustrated with reference to FIGS. 17a and 17 b.

The rectangular coil 20 may also be held in place within the stator 14using a coil holding means implemented as a slotted, cylindrical coilholder that is effectively cut in half (i.e. two half cylindrical coilholders). Other means of holding the coil into place may also be devisedwhile still remaining within the scope of this invention.

In some embodiments, the coil holder 26 may be made from a material thatis not magnetically conductive, such as a plastic material (for exampleDelrin, Nylon or PEEK), however many materials can be used includingthermally-conductive plastics as well as non-magnetically-conductivemetals such as Aluminum. Note that when the coil holder is made from anelectrically-conductive material such as aluminum, eddy currents may beformed in the coil holding means during coil excitation. These eddycurrents have the effect of reducing apparent inductance. However, somedamping of the rotor assembly rotation will also be present since thiscoil holding means will essentially function as a “shorted turn” of theelectrical coil.

When the coil holder 26 is made from a material that is not magneticallyconductive, the actuator 10 is essentially a slotless type of actuator,where the electrical coil turns reside in the air-gap between the magnetand the inside diameter of the stator, thus having similar performanceto conventional optical scanners such as that shown in FIG. 5 and FIG. 6if a similar magnet is used. Here, the magnetic air-gap 15 is relativelylarge. The magnetic field lines 13 that correspond to this configurationcan be seen in FIG. 18, assuming the magnet 32 is a solid cylindricaldiametral-magnetized magnet.

In other embodiments, the coil holder 26 may be made from a materialthat is magnetically conductive, such as the same material used for thestator body 12 (including 1018 steel, 416 or 430 stainless steel, orcarpenter 49). When the coil holder 26 is made from a magneticallyconductive material, the actuator 10 is essentially a slotted type ofactuator, and the electrical coil turns do not reside in the air-gap 15between the magnet 32 and the inside diameter of stator 14. In thiscase, torque production is dramatically improved since the length of themagnetic air-gap 15 is decreased. The magnetic field lines 13 thatcorrespond to this configuration can be seen in FIG. 19, assuming themagnet 32 is a solid cylindrical diametral-magnetized magnet.

If the inside dimensions of the coil holder 26 is implemented in such away that it has a simple circular cross section (with the exception ofslots 50 needed for the coil to fit through), then the actuator 10 willhave a strong tendency to cog toward the outside of the range ofrotation angles. Therefore, “shaping” the interior cross section of thecoil holder may be desirable if it is made from a magneticallyconductive material. One example of this shaping can be seen withreference again to FIG. 17a and FIG. 17b . Here additional slots 52 arecut into the coil holder 26. When a solid cylindricaldiametral-magnetized magnet is used and when the additional slots 52 onthe coil holder 26 are approximately as wide as those slots 50 used tohold the coil, cogging is virtually eliminated. These slots 50, 52 arealso illustrated in FIG. 19.

Although in this example embodiment, the stator 14 is integrally formedwith the actuator body 12 and made from a single material, it is alsopossible to form the stator with laminations, manufactured using anyknown manufacturing technique, such as punching, laser cutting, or photoetching the shape into thin laminations. Moreover, the coil holder 26may also be integrally formed with a stator manufactured in this way,having a slot sufficiently large for the coil 20 to pass through.

As above described, the bore, or herein described hole 16, in the stator14 must be sufficiently large to allow the rotor assembly 18 to fitthrough along with the rectangular coil 20. However, the dimensions ofthis hole 16 also effectively define a maximum outside dimension of theelectrical coil 20. As the hole 16 in the stator 14 is made larger,there is greater room to fit more electrically conductive material (i.e.turns of copper wire) on the electrical coil 20. However, as the hole 16is made larger and the electrical coil 20 is also made larger, thoseturns of wire farthest from the magnet 32 (and closest to the walls ofthe hole in the stator 14) are less productive than the turns of wirethat are closest to the magnet 32. Moreover, if the stator 14 is made ofa magnetic conductive material, increasing the dimensions of the hole 16in the stator 14 also increases the air gap that the flux from themagnet must jump (unless coil holders made of magnetically-conductivematerial are used). This effectively reduces flux density in both themagnet and also in the air gap where the electrical coil resides.

In FIG. 10 through FIG. 14, the position sensor shaft 30 is used alongwith the output shaft 34 for optical scanning applications to desirablyhave positional information. In such a case, a position sensor assembly54 (herein generically illustrated with reference again to FIG. 15)would be used in close proximity to the position sensor shaft. Referenceis made to U.S. Pat. No. 8,508,726 (the disclosure of which is hereinincorporated by reference in its entirety) for examples of the positionsensor assembly 54 useful with embodiments of the invention hereindescribed. However, when position information is not needed or isgathered externally, the position sensor shaft 34 is still of benefit,since it helps to support the magnet 32 and thus, provides additionallateral stiffness.

The output shaft 30 may carry an optical element, such as the mirror asillustrated with reference again to FIG. 1. The optical elements maycomprise a mirror, prism or filter effectively used in optical scanners.

One benefit of the actuator 10 of the present invention is that it isdesirably much less costly to manufacture and has the potential to bemore electrically efficient than typically known actuators. Since thecoil 20 is made in a simple rectangular shape, the coil may be wound oncommon coil winding machines which allow for a very high degree ofcopper packing, while simultaneously producing the coil at very lowcost. The coil 20 is then held in place using the slotted, cylindricalcoil holder 26 which, in some embodiments, may be press-fit into placeor may even be integrally formed with the stator 14 rather than usingadhesive.

In one example actuator 10 currently being manufactured, performance isdesirably good, being generally competitive with the performance ofconventional moving-magnet galvanometers on the current market. In thisexample actuator 10, the actuator body 12 and the stator 14 are formedusing a single piece of 1018 cold rolled steel. The outside diameter ofthe actuator body 12 is 0.5 inches. The hole 16 in the stator is a 6 mmhole. The magnet 32 is made of Neodymium Iron Boron, having a diameteris 0.120 inches and length is 0.315 inches. The output shaft 30 and theposition sensor shaft 34 are each 3 mm in diameter and supported by thetop bearing 22 and the bottom bearing 24 which also have 6 mm outsidediameter so they fit perfectly within the aperture in the stator. Thebearing preload spring 28 applies approximately 6 ounces of force on thebottom bearing 24, keeping balls inside the bearings 22, 24 seated andpreloaded. The rectangular coil 20 has an inside dimension (closest tothe magnet) of 0.132 inches and outside dimension (closest to theaperture in the stator) of 0.224 inches, and having a thickness of 0.070inches. The coil 20 has 100 turns of AWG #36 wire, which provides a coilresistance of approximately 4 ohms. For this actuator 10, when the coilholder 26 is made of a non-magnetically-conductive material, the torqueconstant is 18,000 Dyne*CM per amp of current flowing through the coil.For the actuator 10, when the coil holder 26 is made of amagnetically-conductive material and having inside diameter of 0.160inches, the torque constant is 23,000 Dyne*CM per amp of current flowingthrough the coil. The aperture 40, 42 for the coil 20 to pass through inthe output shaft 30 and the position sensor shaft 34 are sized such thatthe rotor assembly 18 rotates through a 30 degree peak-to-peakmechanical angle.

Although a detailed description and drawings of the invention has beenprovided above, it is to be understood that the scope of the inventionis not to be limited thereby. Further, many modifications and otherembodiments of the invention will come to the mind of one skilled in theart having the benefit of the teachings presented in the foregoingdescriptions and the associated drawings. Therefore, it is understoodthat the invention is not to be limited to the specific embodimentsdisclosed.

1. A limited rotation electromechanical rotary actuator comprising: astator having a bore sized for accepting a rotor assembly and arectangular coil; a rotor assembly bidirectionally operable with thestator over a limited range of rotation, wherein the rotor assemblycomprises an output shaft, a position sensing shaft and a two-polemagnet carried therebetween, wherein the output shaft and the positionsensor shaft are rigidly attached to a peripheral portion of the magnet,and wherein apertures are formed between the magnet and the outputshaft, and between the magnet and the position sensor shaft, theapertures having sufficient size for allowing an electrical coil to passtherethrough; an electrical coil extending around the magnet on foursides thereof, wherein the electrical coil is excitable for providingbidirectional torque to the rotor; and an electrical coil holderreceiving the electrical coil for securing the coil in the bore of thestator.
 2. The actuator according to claim 1, wherein the stator is madefrom magnetically-conductive material.
 3. The actuator according toclaim 1, wherein the stator is made from material that is notmagnetically conductive.
 4. The actuator according to claim 1, whereinthe stator is made of materials including at least one of cold rolledsteel, magnetic stainless steel, and nickel steel.
 5. The actuatoraccording to claim 1, wherein the stator is made of materials includingat least one of at least one of an acetal resin and synthetic polymer.6. The actuator according to claim 1, wherein the coil holder is madefrom material that is not magnetically conductive.
 7. The actuatoraccording to claim 1, wherein the coil holder is made from material thatis magnetically conductive.
 8. The actuator according to claim 1,wherein the coil holder is integrally formed with the stator.
 9. Alimited rotation electromechanical rotary actuator comprising: a statorhaving a bore sized sufficiently to accept a rotor assembly and arectangular coil; a rotor assembly bidirectionally operable with thestator over a limited range of rotation, wherein the rotor assemblycomprises an output shaft, a position sensing shaft and a two-polediametral-magnetized cylindrical magnet carried therebetween, whereinthe output shaft and the position sensor shaft are rigidly attached toat least an outer radial surface of the magnet, the output shaft havinga first aperture for allowing an electrical coil to pass therethroughand the position sensor shaft having a second aperture for allowing anelectrical coil to pass therethrough; and an electrical coil extendinglongitudinally around the magnet, wherein the coil is secured within thebore of the stator, and wherein the electrical coil is excitable forproviding bidirectional torque to the rotor.
 10. The actuator accordingto claim 9, wherein the stator is made from magnetically-conductivematerial.
 11. The actuator according to claim 9, wherein the stator ismade from material that is not magnetically conductive.
 12. The actuatoraccording to claim 9, wherein the stator is made of materials includingat least one of cold rolled steel, magnetic stainless steel, and nickelsteel.
 13. The actuator according to claim 9, wherein the stator is madeof materials including at least one of at least one of an acetal resinand synthetic polymer.
 14. The actuator according to claim 9, furthercomprising a coil holder operable with the coil, wherein the coil holderis made from material that is not magnetically conductive.
 15. Theactuator according to claim 9, further comprising a coil holder operablewith the coil, wherein the coil holder is made from material that ismagnetically conductive.
 16. The actuator according to claim 9, furthercomprising a coil holder carrying the coil, wherein the coil holder isintegrally formed with the stator.
 17. A limited rotation opticalscanner comprising: a stator having a bore sized sufficiently to accepta rotor assembly, top bearing, bottom bearing, a rectangular coil and acoil holder therein; a rotor assembly bidirectionally operable withinthe bore over a limited range of rotation about a longitudinal axis,wherein the rotor assembly comprises an output shaft, a position sensingshaft and a two-pole diametral-magnetized cylindrical magnet affixedtherebetween, wherein the output shaft is rigidly attached to a firstperipheral surface of the magnet and out of contact with a first centralportion of the magnet proximate the longitudinal axis, the output shafthaving a first aperture for allowing an electrical coil to passtherethrough, wherein the position sensor shaft is rigidly attached to asecond peripheral surface of the magnet and out of contact with a secondcentral portion of the magnet proximate the longitudinal axis, theposition sensor shaft having a second aperture for allowing anelectrical coil to pass therethrough, and wherein the longitudinal axispasses through the first and second apertures; and an electrical coilextending longitudinally fully around the magnet and through theapertures, wherein the electrical coil is secured to the stator, andwherein the electrical coil is excitable for providing bidirectionaltorque to the rotor; an electrical coil holder rigidly securing theelectrical coil in place within the stator; and a position sensoroperable with the position sensor shaft.
 18. The actuator according toclaim 17, wherein the stator is made from magnetically-conductivematerial.
 19. The actuator according to claim 17, wherein the stator ismade from material that is not magnetically conductive.
 20. The actuatoraccording to claim 17, wherein the stator is made of materials includingat least one of cold rolled steel, magnetic stainless steel, and nickelsteel.
 21. The actuator according to claim 17, wherein the stator ismade of materials including at least one of at least one of an acetalresin and synthetic polymer.
 22. The actuator according to claim 17,wherein the coil holder is made from material that is not magneticallyconductive.
 23. The actuator according to claim 17, wherein the coilholder is made from material that is magnetically conductive.
 24. Theactuator according to claim 17, wherein the coil holder is integrallyformed with the stator.
 25. An electromechanical, limited rotationrotary actuator comprising: a stator having a bore extending therein; atwo-pole, cylindrical diametral-magnetized magnet extending into thebore and rotatable about a longitudinal axis, wherein the magnet isdefined as having opposing first and second axial ends and a peripheralradial surface extending therearound; a first shaft rigidly affixed tothe magnet by a first connector proximate the first axial end of themagnet and rotatable about the longitudinal axis, wherein a firstaperture is formed between an axial end of the first shaft and the firstaxial end of the magnet; a second shaft rigidly affixed to the magnet bya second connector proximate the second axial end and rotatable aboutthe longitudinal axis, wherein a second aperture is formed between anaxial end of the second shaft and the second axial end of the magnet;and a rectangular toroidal electrical coil fixed within the bore,wherein the coil surrounds the magnet within a plane passing through thelongitudinal axis, the plane passing through the opposing first andsecond ends of the magnet and the peripheral radial surface, wherein theperipheral side of the magnet interacts with opposing active coilportions, and wherein the opposing first and second end-turns of thecoil are carried within the first and second apertures, respectively,and wherein exciting the coil provides limited rotation of the first andsecond connections between the opposing active coil portions, thusproviding limited rotation of the magnet and bidirectional torque to theshafts.
 26. The actuator according to claim 25, wherein the first andsecond connectors extend from a body of the first and second shafts,respectively, and attach to an outer surface of the magnet and areadhesively attached thereto.
 27. The actuator according to claim 25,wherein at least one of the first and second connectors comprisesmultiple connectors.
 28. The actuator according to claim 25, wherein thefirst and second apertures provide free space between the shaft and thecoil and between the coil and the magnet.
 29. The actuator according toclaim 25, wherein a gap is formed around the magnet between the coil andinner portion of the coil.
 30. The actuator according to claim 25,wherein the first and second apertures are formed within the opposingfirst and second axial ends of the magnet.
 31. The actuator according toclaim 25, further comprising a coil holder operable with the stator forsecuring the electrical coil to the stator.
 32. The actuator accordingto claim 31, wherein the coil holder comprises a a tube having firstslots on diametrically opposed sides thereof sufficient for fixing thecoil therein.
 33. The actuator according to claim 32, wherein the coilholder further comprises second slots, wherein the second slots areapproximately as wide as the first slots holding the coil, thus reducingcogging.
 34. The actuator according to claim 25, wherein the firstconnector and second connector are attached to the magnet on oppositesides thereof.
 35. The actuator according to claim 25, wherein the firstconnector comprises a multiple connectors attached to the magnet.